The objective of this proposal is to develop a simple practical but rational system for clinical genetics especially genetic counseling and its eugenic consequences. A number of individual topics are listed. They include consanguinity (incorporating posterior and provisional posterior information); age-dependence (which is being dealt with by a three-compartmental model, latency-manifestation-removal); and incomplete penetrance in the face of ascertainment bias. The statistical properties, notably the power of the mixed model will be explored with special relationship to the Roberts' correction. The eugenic impact of changes in the patterns of reproduction as a result of policies or spontaneous responses of consultants to better knowledge and understanding making use of branching models. The efficiency of these methods will be tried out in practice with the aid of a genetic counselor.